1. Field
Embodiments of the present disclosure relate to circuit simulators and analysis of circuits. More specifically, embodiments of the present disclosure relate to a technique for estimating crosstalk-induced time delay in a signal path using random variables for individual crosstalk aggressors.
2. Related Art
When crosstalk is present between signal nets or paths, their effect on the delay values computed during timing analysis is often determined on a stage-by-stage basis (where each stage includes at least one driver coupled to at least one receiver). Furthermore, in order to detect potential timing violations, worst-case values are often used for the time-delay contributions from each of the stages.
However, using worst-case values for the time-delay contributions is typically too conservative because during a given clock cycle some crosstalk aggressors may not switch, may switch in opposite directions, and/or may not switch at exactly the desired time. Hence, the probability that the worst-case delay value will occur during normal operation is typically very small. Consider an example where there are four crosstalk aggressors per stage in a ten-stage signal path. Suppose that the probability of a given crosstalk aggressor switching is 50% and that the probability of its switching in the opposite direction of the victim is 50%. Then the probability of occurrence of the worst-case crosstalk time delay on the signal path would be (0.5−0.5)−40, which corresponds to an unreasonably high mean time to failure of 38,300,000 years.
In an attempt to reduce the pessimism of such worst-case-based time-delay analysis, some approaches model the time-delay contributions from each of the stages as statistical random variables. However, the total path delay calculated using such approaches is still typically too conservative. Consequently, circuit designers may end up redesigning circuits to fix timing violations which are not likely to occur during normal operation, thereby increasing the time and cost for designing circuits.
Hence, there is a need for an analysis technique that calculates crosstalk-induced time delay without the above-described problems.